This invention relates to a power failure-free power supply apparatus, and more particularly to a power failure-free power supply apparatus increased in operational reliability.
A computer has been increasingly involved in daily life. Incorporation of a computer in an important system does not permit any shutdown of the system in order to avoid damage to the computer. Also accidental power failure possibly causes damage to a software of a computer. Thus, a computer is generally equipped with a power failure-free power supply apparatus to prevent power failure of a commercial power supply from adversely affecting the computer, so that feed to the computer may be ensured irrespective of power failure of the commercial power supply.
A conventional power failure-free power supply apparatus is disclosed in Japanese Patent Application Laid-Open Publication No. 285135/1997. Now, the conventional power supply apparatus will be described with reference to FIG. 5. In FIG. 5, reference numeral 1 designates an AC power supply, for which a commercial power supply is generally used. 2 is a power rectifier, 3 is a power inverter, 4 is a power rectifier/inverter, 6 is a load, and 7 is a storage battery. The power rectifier 2 is connected to the AC power source 1 and the power inverter 3 is connected to the load 6 through selection switches SB1 and SC1. The power rectifier/inverter 4 is connected through a selection switch AS 1 to the AC power supply 1, as well as through switches SA2 and SB" and the selection switch SC1 to the load 6. Also, the AC power supply 1 is connected through a selection switch SC2 to the load 6. The converters 2, 3 and 4 each have a DC terminal connected to the storage battery 7.
The conventional power failure-free power supply apparatus thus constructed is basically operated according to a normal operation mode, an operation mode during power failure, an operation mode during failure of the power inverter and an operation mode during failure of the power rectifier.
The normal operation mode is an operation mode wherein the power rectifier 2 and power inverter 3 are operable. The selection switches SB1, SC1 and SA2 are kept closed and the selection switches SA1, SB2 and SC2 are kept open. The power rectifier 2 converts AC power of the AC power supply 1 into DC power to feed it to the power inverter 3 and charge the storage battery 7. The power inverter 3 feeds AC power to the load 6. The power rectifier/inverter 4 carries out stand-by operation in reserve when any failure occurs in the power inverter 3.
The operation mode during power failure is an operation mode carried out when power failure occurs in the AC power supply, wherein power discharged from the storage battery 7 is fed to the load 6. When power failure occurs in the AC power supply 1, the power rectifier 2 is kept from operation and the power inverter 3 converts DC power obtained due to discharge of the storage battery 7 into AC power to feed it to the load 6. At this time, the power rectifier/inverter 4 carried out stand-by operation which permits DC power of the storage battery 6 to be converted into AC power.
The operation mode during failure of the power inverter is an operation mode carried out in the case that failure occurs in the power inverter 3 which feeds the load 6. When failure occurs in the power inverter 3, the selection switch SB1 is rendered open and the selection switch SB is closed, resulting in the power rectifier 4 which has carried out stand-by operation feeding AC power to the load 6. After repair or replacement of the power inverter 3, the selection switch SB is rendered open and the selection switch is closed, so that the power supply apparatus may be returned to the normal operation mode.
The operation mode during failure of the power rectifier is an operation mode taking place when failure occurs in the power rectifier 2. When the power rectifier fails, the power inverter 3 converts DC power of the storage battery 7 into AC power to feed it to the load 6. The selection switch SA2 is open to permit the power rectifier/inverter 4 which has carried out stand-by operation to act as a power rectifier for converting AC power into DC power, resulting in the switch AS 1 being closed. This permits the storage battery 7 to be charged from the AC power supply 1 through the power rectifier/inverter 4 and DC power to be fed to the power inverter 3. After repair of the power rectifier 2, the selection switch SA1 is rendered open to permit the power rectifier/inverter 4 to carry out power rectification, leading to turning-on of the selection switch SA 2, so that the apparatus may be returned to the normal operation mode.
The operation mode during a plurality of failures is an operation mode carried out when failure occurs in two of the conversion units 2, 3 and 4. The election switches SC1 and SC2 are open and closed, respectively, resulting in AC power being fed from the AC power supply 1 directly to the load 6. After failure of the converters is repaired, the apparatus is returned to the normal operation mode.
The mode of charging the storage battery increased in capacity is an operation mode taking place when the storage battery increased in capacity to a degree sufficient to permit the load to satisfactorily operate during power failure of the AC power supply over a long period of time is charged. An increase in capacity of the storage battery 7 causes much power to be required to charge the battery 7, so that charging of the storage battery using only the power rectifier 2 having a capacity determined depending on a capacity of the power inverter 3 requires much time. Thus, charging of the storage battery 7 is carried out by changing over a mode of the power rectifier/inverter 4 into a power rectifier mode and subjecting the units 4 and 2 to parallel operation. This permits power for charging the storage battery 7 to be doubled.
However, it was found that the conventional power failure-free power supply apparatus has several problems.
More particularly, incorporation of the storage battery increased in capacity into the power supply apparatus permits the power rectifier/inverter to carry out power rectifying operation, to thereby subject the power rectifier and power rectifier/inverter to parallel operation, resulting in a charging current to the storage battery being increased. The parallel operation fails to permit the power rectifier/inverter to be in reserve for the power inverter, resulting in operational reliability being deteriorated as compared with during normal operation wherein the power rectifier/inverter carries out power inverting operation for stand-by operation. Thus, it is required to increase the charging current as much as possible to rapidly charge the storage battery during the parallel operation. Unfortunately, the prior art fails to fully consider that the charging current is increased during the parallel operation.
There occurs a difference in converted power between the parallel operation of the power rectifier/inverter and power rectifier and sole operation of any one of both. However, when a charging current of the storage battery is subject to restriction so that the converted power of the power rectifier for charging the storage battery during the normal operation does not exceed a capacity of the power rectifier or is not excessive, the charging current when the parallel operation is carried out is limited to a level twice as high as the charging current fed by only the power rectifier. Thus, the parallel operation fails to effectively utilize a sum of capacities of the power rectifier/inverter and power rectifier, even when the sum is surplus.